Substrate with perfluorocarbon polymeric coatings having low critical surface tensions

ABSTRACT

Polymers comprising pendant amine-functional portions linked to a perfluorocarbon moiety having a perfluoroalkyl group. Such polymers can provide coating compositions which exhibit critical surface tensions of wetting of less than about 15 dynes/cm.

BACKGROUND OF THE INVENTION

This invention relates to novel perfluorocarbon based polymericmaterials useful as release coatings and to processes for using suchcoatings as mold release agents.

A wide variety of molding applications require molding apparatus withsurfaces which will easily release molded articles and moldingmaterials. Polymer deposits on molding apparatus surfaces resulting fromthe "sticking" occurring during molding processes not only make it moredifficult and time consuming to remove molded parts from said molds, butsuch deposits have a tendency to deteriorate and fragment, thusdecreasing the quality of the surfaces of products molded therefrom.

One approach directed towards obtaining surfaces which readily releaseadhesives has involved the application of various hydrocarbon andsilicone oils and waxes to the surfaces of molds which are exposed tosaid polymer compositions. Commonly, hydrocarbon and silicone oils andwaxes are sprayed or wiped onto injection molding apparatus, which isthen used for the molding of polymers and prepolymers. Unfortunately, itis generally the case that only one to about three injection cycles maybe performed before it is necessary to retreat the mold with saidnonstick agents.

Another approach for providing molding apparatus surfaces which havegood release characteristics is the application of fluorinated polymers,such as tetrafluoroethylene. These types of polymers are typicallyapplied to a surface as small solid particles or as a coating.Unfortunately, these types of polymers are typically bound to surfaceswith nonfluorinated binders or by a difficult process involvingsintering of the polymer particles at high temperatures.

Perfluorinated polymers are believed to release because they produce avery low critical surface tension of wetting (γ_(c)). More recently, asdisclosed in U.S. Pat. No. 4,344,993, a combination of a hydrophilicpolymer with up to about 0.5 weight percent perfluorocarbon andcrosslinked with a cyclic sulfonium zwitterion yields a surface coatinghaving a surface tension of wetting of less than that of coatingsconsisting of 100 percent perfluorocarbon. Although this type of coatingis useful for preventing deposits of nonaqueous polymerization reactantsand products from adhering to reactor surfaces in the production ofolefinic polymers, such a coating does not adhere adequately to surfacesof conventional molding apparatus when amounts of perfluorocarbongreater than 0.5 weight percent are employed.

Therefore, it is highly desirable to provide an improved coating whichadheres well to a molding apparatus surface, and a process for usingsame which will significantly reduce the undesirable deposition ofmaterial and sticking on internal surfaces of molding apparatus byproviding a low γ_(c).

SUMMARY OF THE INVENTION

The present invention is a polymer comprising pendant amine-functionalportions linked to a perfluorocarbon moiety having a perfluoroalkylgroup through a carboxy functionality.

In another aspect, the present invention is an adherent coatingcomposition comprising the polymer of this invention.

The amount of perfluorocarbon moiety present in the polymer is such thatthe resulting coating can exhibit a critical surface tension of wettingof less than about 15 dynes per centimeter (dynes/cm). Surprisingly, theperfluorocarbon-containing polymer coating composition of the presentinvention can provide a surface having a critical surface tension lessthan that of a coating consisting entirely of a linear perfluorocarbon,such as a homopolymer of tetrafluoroethylene. The coating composition ofthis invention provides a permanently bound coating which can be easilyapplied, and which is not removed or wet by most solvents.

In another aspect, the present invention is a composition comprising apolymer comprising aminefunctional portions, a nucleophilicfluoroalkyl-containing carboxylic acid, and a suitable solvent. Whencured, said composition yields the aforementioned adherent coatingcomposition, as defined hereinbefore. In yet another aspect, thisinvention is a coated substrate wherein said composition is contactedwith the substrate and cured.

The coating compositions of this invention are particularly useful inreducing the amount of sticking of material on the internal surfaces ofthe molding apparatus. Accordingly, in another aspect, this invention issuch a process for reducing the sticking of material to surfaces such asinternal surfaces of molding apparatus which comprises applying asolution of the aforementioned composition to the internal surfaces ofmolding apparatus and curing. Such a process is advantageously employedin the molding of polymers such as polyethylenes, polypropylenes,polycarbonates, polyurethanes, and the like.

DETAILED DESCRIPTION OF THE INVENTION

The polymer comprising pendant amine-functional portions of thisinvention have repeating units of the general formula: ##STR1## whereinA is hydrogen, chloride or methyl; and Z is a bridging group containingat least one carbon atom and which can contain oxygen, nitrogen and/orsulfur atoms. Examples of suitable monomers useful in preparing thepolymers of this invention include acrylamide, 2-aminoethylmethacrylate,vinylbenzylamine, and the like.

Polymers of this invention are generally represented by the formula:##STR2## wherein a+b+c+d=1, a is greater than 0, b is from about 0 toabout 0.9, c is from about 0 to about 0.9, d is from 0 to about 0.8, andm is preferably about 100 to about 10,000. A is H, chloride or methyl.Y¹ is as defined hereinafter. Z is a bridging group containing at leastone carbon atom. R_(F) is saturated perfluoroaliphatic containing moietyas described hereinafter. X can vary and is preferably an essentiallynonionic moiety or an ionic moiety. X can include, for example, a moietyderived from butadiene, isoprene, ##STR3## wherein R is hydrogen oralkyl comprising from 1 to about 12 carbon atoms. Y is the remainingportion of a polycarboxylic acid or other species containing an acidichydrogen and is present in such a way that crosslinking is introduced tothe polymer system. R_(A) is an alkyl or aryl moiety as definedhereinafter.

Polymers of this invention are advantageously prepared by reactingmonomers having pendant aminefunctionalities and optionally othermonomers in order to obtain a polymer comprising pendant aminefunctionalities. The polymer is contacted with aperfluoroalkyl-containing acid and optionally, the other acids asdefined hereinafter. The mixture is then subjected to conditions suchthat the acid functionality reacts with an oxazoline or oxazinefunctionality to form an amidetype linkage.

Crosslinking can be introduced to the polymer with a polyfunctionalnucleophilic species such as carboxylic acid. Low equivalent weightpolyfunctional carboxylic acids are preferred. Preferred polyfunctionalcarboxylic acids are the di- and tri-carboxylic acids. Examples ofdi-carboxylic acids include those represented by the formula: ##STR4##wherein t can range from 1 to about 40. The amount of crosslinking canvary and is employed in order to form a harder, more rigid product.Other suitable polyfunctional nucleophilic species include the aromaticcarboxylic acids such as terephthalic acid, unsaturated carboxylicacids, and the like.

Moieties designated as R_(A) generally are any alkyl or aryl moietieshaving functionalities which can be reacted with a pendant amine moietyto yield a pendant grouping. For example, R_(A) can be derived from acarboxylic acid having from about 4 to about 25 carbon atoms.

Perfluoroalkyl-containing acids suitably employed in the practice ofthis invention include organic compounds represented by the formula:

    R.sub.F -Y.sup.1 -COOH

wherein R_(F) is a perfluorocarbon or a saturated perfluoroaliphaticmoiety containing a F₃ C-- moiety and is linked to the carboxylic acidmoiety through a moiety which does not substantially interfere with thenucleophilicity of the carboxy group, (i.e., Y¹) advantageously ahydrocarbon moiety preferably containing at least 2 carbon atoms. Theperfluoroaliphatic or perfluorocarbon moiety advantageously containsfrom about 3 to about 18 carbons wherein substantially all are fullyfluorinated, preferably from about 3 to about 14, more preferably fromabout 3 to about 10 of such carbons subject to the limitation that thefluoroaliphatic moiety is linked to the carboxylic acid moiety throughan aliphatic hydrocarbon moiety (i.e., Y¹) containing at least 2 carbonatoms. R_(F) can be linear, branched or cyclic, preferably linear. Y¹contains a carbon-bonded hydrogen and can contain an oxygen atom, sulfuratom and/or a nitrogen atom bonded only to carbon atoms in the skeletalchain. More preferable are those linear perfluoroaliphatic moieties(i.e., R_(F)) represented by the formula: C_(n) F.sub. 2n+1 wherein n isin the range of about 3 to about 10. Most preferred are those linearperfluoroaliphatic moieties represented in the paragraph below.

Perfluorocarbon containing carboxylic acids of the formula CF₃ (CF₂)_(p)SO₂ NH(CH₂)_(q) COOH; wherein p is from about 2 to about 15, preferablyabout 2 to about 9, and q is from about 2 to about 4 are preferred. Anespecially preferred perfluorocarbon containing carboxylic acid is thecarboxylic acid form of the perfluorocarbon sold by DuPont under thetrade name Zonyl® FSA; or the carboxylic acid form of theperfluorocarbon sold under the trade name Fluorad® FC 129 by the 3MCorporation. Examples of other preferred anionic perfluorocarbonstarting materials, as well as methods of preparation, are illustratedin U.S. Pat. Nos. 3,172,910 and 3,630,951.

The polymer containing pendant amine-functionalities is advantageouslycontacted with a nucleophilic, fluoroalkyl-containing carboxylic acid inthe presence of a liquid that is a solvent for each of the species(i.e., a suitable solvent). Typically, such solvents include thealkanols such as ethanol, propanol, butanol, glycols, mixtures ofsuitable alkanols and mixtures of alkanols with water. If desired,aqueous ammonia can be added to the formulation in order to increase theshelf life of the mixture. In particular, the pendantamine-functionality undergoes a reaction with the fluoroalkyl-containingacid to apparently produce an amide-type linkage. The reaction isinitiated, for example, by heat and/or loss of solvent after thepolymer, fluoroalkyl-containing acid and solvent as applied to thesurface of the substrate which is being treated.

Accordingly, the coating composition can be applied directly (i.e.,without the prior application of a primer coating) to the interiorsurfaces of the molding apparatus in a convenient manner, such aswiping, spraying, brushing on, and the like. Brushing has been found tobe satisfactory since it ensures complete coverage of all surfaces. Anyuncovered areas, such as pinholes, etc., should be avoided since suchexposed areas provide sticking sites for polymer build-up. It is mostdesirable that one layer of coating be applied. The amount of coatingapplied for the thickness thereof is not partioularly critical so longas a continuous film over all interior surfaces of the molding apparatusis provided. In some instances, it is preferable to pretreat theinternal surfaces of the reaction vessel with conventional chemicalcoupling agents. For example, prehydrolyzed silane coupling agents suchas ##STR5## and the like are particularly useful for this purpose.

When said coating compositions are applied to the surface of a moldingapparatus and cured, the resulting coatings are (1) inert to anypolymeric reagents which will contact the coating in subsequent use, (2)can have a γ_(c) of less than about 15 dynes/cm, and (3) will not wetwith any common solvents.

Following the application of the coating composition of the interiorsurfaces of the mold, including product transfer conduits, etc., thecoating can be heated in order to dry and cure the same. Any suitableheating method can be employed, such as radiant heating, heated air, andthe like. Usually, temperatures within the range of 90° to about 160° C.are sufficient; with temperatures in the range of 110° to 160° C. beingpreferred. The temperature chosen will depend upon the time of drying.Thereafter, the molding to be carried out in the equipment can becommenced immediately. No particular modifications of processingtechniques are required due to the presence of the coating. Further,utilization of the internally coated mold of the present invention doesnot adversely affect the heat stability or other physical and chemicalproperties of the polymers or other molded products produced therein.Ordinary care should, of course, be exercised to avoid abrading orrupturing the coating.

Compositions of this invention can be applied to fabrics such as cottonand nylon. For example, compositions of this invention are useful intreating fabrics in order to provide water and/or oil resistance to thefabric. See, for example, U.S. Pat. Nos. 4,325,857 and 4,388,372.

The following examples are illustrative embodiments of this inventionand should not be construed as limiting its scope. Unless otherwiseindicated, all parts and percentages are by weight.

EXAMPLE 1 Preparation of Poly 2-Aminoethylmethacrylate (Poly AEM)

Water (100 g) is added to 83.3 g of a 30 percent solution of AEMhydrochloride and the solution is placed in a stirred reactor undernitrogen and warmed to 50° C. Two solutions, A and B are added in 1.5 mlportions every 5 minutes for about 1 hour and the reaction is allowed tocontinue for about 6 hours at 50° C. Solution A contains 0.1 g oftert-butyl hydroperoxide in 18 ml of water and solution B contains 0.075g sodium formaldehyde hydrosulfite, sold as Formapon® by the Rohm & HaasCorporation, in 18 ml of water. The resulting Poly AEM hydrochloride isexchanged to the free amine with hydroxyl functionalized ion exchangeresins.

Preparation of Coatings Based on Poly AEM

A coating solution is prepared by mixing 1.0 g of a 13.4 percent watersolution of Poly AEM (1.04 mil eq.) with 3 g of diethylene glycol methylether, 0.05 g aqueous ammonia (29.2 percent ammonia) followed by 1.30 gof a 0.8N solution (1.04 mil eq.) of CF₃ --F₂)_(x) CH₂ CH₂ -S-CH₂ CH₂COOH (x=3 to 18), acid form of Zonyl® in Dowanol DM. The resultingsolution is cast on a microscope slide and cured at 160° C. for 45minutes to yield a 4-H pencil hardness that does not wet with hexane,acetone, methanol or water.

EXAMPLE 2 Preparation of Coatings Based on Poly AEM

A coating formulation is prepared by mixing 1.0 g (1.04 mil eq.) of 13.3percent Poly AEM (in water) with 0.05 g aqueous ammonia (29.2 percentammonia) 3 g diethylene glycol methyl ether, 1.0 g of 0.8N (Zonyl® Acid)(0.8 mil eq.) and 0.1 g of 2N malonic acid in water (0.2 mil eq.). Theresulting coating is cured on a microscope slide at 160° C. for 45minutes to yield a coating with a pencil hardness of greater than 6-H.This coating does not wet with hexane, methanol, acetone or water.

EXAMPLE 3 Polyvinylbenzylamine (Poly VBA)

A solution of 40 g VBA in 350 ml water is adjusted to pH 7 withhydrochlorine acid and warmed under nitrogen to 65° C. With stirring 0.2g of 2,2'(2-methylpropionitrile) is added. After 5 hours the resultingpolymer solution is exposed to high speed mixing and concentratedaqueous ammonia is added. The solid polymer is washed 5 times with waterand dissolved in ethylene glycol dimethyl ether.

Preparation of a Coating Based Upon Poly VBA

A coating solution is prepared by mixing 2.0 g of a 5.05 percent PolyVBA (0.75 mil eq.) in diethylene glycol methyl ether with 0.075 gaqueous ammonia (29.2 percent ammonia) and 0.875 g of 0.80N Zonyl® FSAAcid (0.70 mil eq.) in diethylene glycol methyl ether. The solution iscast on a microscope slide and cured at 160° C. for 30 minutes. Theresulting coating has a pencil hardness of greater than 6-H and acritical surface tension of wetting of between 12 and 13 dynes/cm.

What is claimed is:
 1. A coated substrate wherein the coating for thesubstrate results from contacting the composition comprising a polyaminecontaining polymer, a nucleophilic fluoroalkyl-containing carboxylicacid and a suitable solvent with said substrate and curing to yield apolymer comprising pendant amine-functional portions, having repeatingunits of the general formula ##STR6## wherein A is selected from thegroup consisting of the hydrogen, chloride and methyl radicals; and z isa bridging group containing at least one carbon atom and which cancontain oxygen, nitrogen and/or sulfur atoms, linked to aperfluorocarbon moiety having a perfluoroalkyl group through a carboxygroup.